effect of dividing lines on design ratio

[Nastaran1]

I'm using SAP2000 in order to design a structure. I want to compare SAP results with another software so that I should divide lines (members). But design ratios changed a lot when I divide them and I don't understand what is the reason...

 

[Erik Panos Kostson]

I am not familiar with the software at all (with the exception that the software I use can import SAP2000 files, but that is about it).

In the manual I think there should be a section (in the relevant code/standard that you are using) called "Effects of Breaking a Member into Multiple Elements". (I know there is such a section for the Russian steel code in SAP2000). For example what could happen is that the effective lengths are not picked up correctly when a member (e.g., beam, column) is split up in to many finite elements, hence many buckling checks might be off.

That might give some ideas why the results are different.

Hopefully someone else will have some more feedback.

 

[JasonMcKee71]

It calculates effective lengths incorrectly and therefore design results may not be expected ones.

Jason McKee
proud R&D Manager of
Cross Section Analysis & Design
Software for the structural design of cross sections
Moment Curvature Analysis
Interaction Diagrams
Reinforcement Design etc.

 

[Nastaran1]

Thanks all for the replies.

I think when the members are shorter, design coefficient should be lower. but now it is larger. do you know what is the reason?

(I want to compare the results with RSTAB software so I forced to break the elements)

 

[Agent666]

How does it compare to your hand checks?

When you divide the members usually an analysis program can better account for 2nd order little P delta forces. Hence this affects buckling effective lengths, and hence capacities.

 

[271828]

As Agent666 mentioned, perform manual calculations and compare those to the computer output.